The present invention relates to the extraction of metals from ore, and more particularly to a process for extracting metals from ore wherein the ore is exposed to a particular gaseous environment such that the metals react with a reactive gas in the environment, extracting metals from the ore as salts.
The extraction of metals from ore can be performed by a number of mechanical and chemical processes known in the mining industry. These processes included leaching, panning and other methods of gravity separation, centrifugal separation, electro-chemical reduction and similar known methods of process metallurgy. These various processes have generally proven economically successful when used on ore wherein the metal particles are large, and also when the metal values (i.e. concentrations of the metals as a percentage of the ore) are high. These known processes become uneconomical when the metal particles become too small or the metal values in the ore become too small. The present invention is a new process which uses a plasma for extracting metals from ore. The process of the present invention can economically extract smaller particles and smaller metal values than previous known processes.
Plasmas are electrically neutral, highly ionized gasses which can be generated by electrically heating a low-pressure gas. While plasmas exhibit microscopic properties much like ordinary gasses, plasmas also exhibit collective or fluid-like properties which are markedly different from ordinary gasses. Plasmas can conduct electricity, are responsive to magnetic fields, and can propagate various kinds of waves. Plasmas may exist in an uncontrolled, freely changing form, or may be carefully regulated and constrained between electrodes in a constant maintained form. Examples of uncontrolled plasmas include lightning and arc welding, and an example of a controlled plasma is fluorescent lighting.
While plasmas have been used for a variety of purposes, they are particularly useful as a source of high intensity heating, such as in arc welding. However, as the extraction of metals from ore has generally been performed using low temperature processes, the heating and other effects of plasmas have not generally been used in process metallurgy.
Plasmas have been used as a source of high intensity heat to vaporize fine particle products in recovery of valuable metals from slag or low grade concentrate. U.S. Pat. No. 3,989,512 to Sayce discloses use of a column of uncontrolled plasma projected from jets in this manner. A low grade tin concentrate may be fed as a stream of fine particles born in a carrier gas stream into the plasma column. The particulate material is heated to temperatures of 1,600.degree. to 2,000.degree. C., thereby vaporizing tin from the particulate into stannic oxide fume.
The temperatures involved in using the uncontrolled plasma jets described by the Sayce patent create particular problems. The material of the plasma inducing electrode may itself volatilize, stopping the reaction process. The Sayce patent suggests surrounding the electrodes with an inert gaseous environment such as argon or nitrogen to limit volatilization of the electrodes. The electrodes and the surrounding structure of the device used must be made of materials which can withstand the high temperature created by the plasma.